diff options
| author | Steve Kargl <sgk@troutmask.apl.washington.edu> | 2021-02-08 19:45:30 +0000 |
|---|---|---|
| committer | Dimitry Andric <dim@FreeBSD.org> | 2021-02-15 18:08:20 +0000 |
| commit | 720600023287cd029894b79477fb2bd4a5183ba4 (patch) | |
| tree | 44615447c7bfc3d04b7abea06ea4fc0fd266ec37 | |
| parent | 78968ce3ddbf56ac7f7b548cfe8d39707f9989d8 (diff) | |
Fix incorrect powf(3) result with x near 1 and |y| much larger than 1
This adjusts the check to trigger overflow/underflow to a slightly lower
value.
Before: powf(9.999995e-01, -1.342177e+08) -> inf
After: powf(9.999995e-01, -1.342177e+08) -> 1.858724e+31
(cherry picked from commit 93fc67896550548f91b307dbe3053f11db5d4a8a)
Add test case for 93fc67896550 (incorrect powf(3) result)
This adds the test case to contrib/netbsd-tests/lib/libm/t_pow.c, as it
is currently the only place testing pow(3) and friends.
(cherry picked from commit 51af03328755c9095e94d20858a8d10acfe412ae)
| -rw-r--r-- | contrib/netbsd-tests/lib/libm/t_pow.c | 22 | ||||
| -rw-r--r-- | lib/msun/src/e_powf.c | 2 |
2 files changed, 23 insertions, 1 deletions
diff --git a/contrib/netbsd-tests/lib/libm/t_pow.c b/contrib/netbsd-tests/lib/libm/t_pow.c index 7afee9f6dffa..09e72be7311b 100644 --- a/contrib/netbsd-tests/lib/libm/t_pow.c +++ b/contrib/netbsd-tests/lib/libm/t_pow.c @@ -637,6 +637,27 @@ ATF_TC_BODY(powf_zero_y, tc) } } +ATF_TC(powf_near_one_x_huge_y); +ATF_TC_HEAD(powf_near_one_x_huge_y, tc) +{ + atf_tc_set_md_var(tc, "descr", "Test powf(->1, huge) != inf"); +} + +ATF_TC_BODY(powf_near_one_x_huge_y, tc) +{ + const float x = 0x1.ffffeep-1f; /* 9.999995e-01f */ + const float y = -0x1.000002p+27f; /* -1.342177e+08f */ + const float e = 0x1.d53532p+103f; /* 1.858724e+31f */ + const float ulp = __FLT_EPSILON__; + float z; + + z = powf(x, y); + + ATF_CHECK(isinf(z) == 0); + ATF_CHECK(fabsf(z - e) <= 2 * ulp); +} + + ATF_TP_ADD_TCS(tp) { @@ -661,6 +682,7 @@ ATF_TP_ADD_TCS(tp) ATF_TP_ADD_TC(tp, powf_one_pos_x); ATF_TP_ADD_TC(tp, powf_zero_x); ATF_TP_ADD_TC(tp, powf_zero_y); + ATF_TP_ADD_TC(tp, powf_near_one_x_huge_y); return atf_no_error(); } diff --git a/lib/msun/src/e_powf.c b/lib/msun/src/e_powf.c index 53f1d37d6bec..33eedad50b16 100644 --- a/lib/msun/src/e_powf.c +++ b/lib/msun/src/e_powf.c @@ -136,7 +136,7 @@ __ieee754_powf(float x, float y) /* |y| is huge */ if(iy>0x4d000000) { /* if |y| > 2**27 */ /* over/underflow if x is not close to one */ - if(ix<0x3f7ffff8) return (hy<0)? sn*huge*huge:sn*tiny*tiny; + if(ix<0x3f7ffff7) return (hy<0)? sn*huge*huge:sn*tiny*tiny; if(ix>0x3f800007) return (hy>0)? sn*huge*huge:sn*tiny*tiny; /* now |1-x| is tiny <= 2**-20, suffice to compute log(x) by x-x^2/2+x^3/3-x^4/4 */ |